To burn the most calo­ries, it helps to heed clock

The Buffalo News - - FRONT PAGE - By Melissa Healy LOS AN­GE­LES TIMES

LOS AN­GE­LES – Next time you stagger into a Waf­fle House in the wee hours of the morn­ing and or­der the Texas sausage egg & cheese melt (1,040 calo­ries), con­sider this new re­search find­ing: At roughly that hour, the most ba­sic op­er­a­tions of the hu­man body throt­tle back their caloric needs by about 10 per­cent com­pared to the rate at which they will burn calo­ries in late af­ter­noon or early evening.

Maybe you’d pre­fer to come back around din­ner­time.

This pat­tern of calo­rie use doesn’t sig­nif­i­cantly vary based on whether you’re the wait­ress work­ing the grave­yard shift or a 9-to-5’er stop­ping in for break­fast af­ter eight hours of shut-eye, the re­searchers found. Hu­mans’ “rest­ing en­ergy ex­pen­di­ture” – the body’s use of calo­ries to power such ba­sic func­tions as res­pi­ra­tion, brain ac­tiv­ity and fluid cir­cu­la­tion – fol­lows a pre­dictable cy­cle that waxes as the day pro­gresses and wanes as night sets in.

The new study, pub­lished this week in the jour­nal Cur­rent Bi­ol­ogy, of­fers fur­ther ev­i­dence that cir­ca­dian rhythms dic­tate not just when we feel the urge to sleep but how com­plex mech­a­nisms like me­tab­o­lism op­er­ate across a 24-hour pe­riod. It may help ex­plain why peo­ple who keep ir­reg­u­lar sleep sched­ules, in­clud­ing swing shift work­ers, have higher rates of obe­sity and are more likely to de­velop metabolic ab­nor­mal­i­ties such as type 2 di­a­betes.

And it demon­strates that whether we hear it or not, our body’s clock is al­ways tick­ing, lo­cat­ing us in our daily cy­cle with un­canny pre­ci­sion.

At “hour zero” – roughly cor­re­spond­ing to some­where be­tween 4 and 5 a.m. – our core body tem­per­a­ture dips to its low­est point and our idling fuel use reaches its nadir. From that point, at first quickly and then a bit more slowly, the body’s “rest­ing en­ergy ex­pen­di­ture” rises un­til the late af­ter­noon/early evening. Af­ter reach­ing its peak at roughly 5 p.m., the num­ber of calo­ries we burn while at rest plum­mets steadily for about 12 hours.

And then, just as surely as day fol­lows night, we start again.

Th­ese new find­ings are a re­minder that no mat­ter how 24/7 our sched­ules have be­come, our bod­ies were built for a slower, sim­pler world in which hu­mans moved around all day in search of food, ate while the sun was up, and slept when the sky was dark.

To­day, our ap­petites and the all­night avail­abil­ity of tempt­ing food may in­duce us to eat well af­ter sun­down. And our jobs may de­mand that we sleep dur­ing the day and wait ta­bles, care for pa­tients or drive trucks through the night. But our bod­ies still ad­here to their an­cient, in­flex­i­ble clocks. The study’s find­ings also come with an im­plicit warn­ing: When we dis­re­gard the bi­o­log­i­cal rhythms that rule our bod­ies, we do so at our peril.

The new study adds to a grow­ing body of ev­i­dence sug­gest­ing that a good 12-hour fast, when aligned with dark­ness and our bod­ies’ noc­tur­nal re­sponse, may be a way to pre­vent or re­verse obe­sity.

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